Pneumorrhachis following cervical spine surgery

Summary

A 66‐year‐old man experienced symptomatic pneumorrhachis (air within the spinal canal) following a cervical laminoplasty for the excision of meningioma. Following an uneventful intraoperative course, he suffered a fluctuating hemiparesis of varying severity. Urgent imaging demonstrated extradural and intradural air in the spinal canal. Treatment with supplemental oxygen and dexamethasone was commenced, and the patient’s symptoms improved over a period of three days with full resolution at six weeks. Pneumorrhachis can be avoided by allowing air to escape from the spinal canal through positioning, and displacement with irrigation fluid at the time of wound closure. However, if pneumorrhachis does occur, oxygen therapy, positioning of the patient to mitigate the gravitational effect of the air bubbles and supportive treatment are the central elements of management. Other possible causes of neurological deficit should be ruled out. This is particularly important as treatment options for some differential diagnoses can potentially cause harm if started based on clinical impression alone, for example, re‐exploration for suspected haematoma. Only a small number of previous reports have described symptomatic pneumorrhachis as a complication of spinal surgery. This patient was successfully managed with conservative measures following the exclusion of other spinal cord pathologies.

Introduction

Pneumorrhachis is a term used to describe air within the spinal canal [1]. It usually occurs following an intentional durotomy (as in our case) or an unintentional dural tear. The incidence of unintentional dural tears during spinal surgery ranges from 0.3% to 5.9%; however, the occurrence of pneumorrhachis and pneumocephalus remain extremely rare [2].

Due to the low incidence of symptomatic pneumorrhachis, the pathophysiology and management of the condition are not widely recognised. Air can distribute within the spinal intrathecal (i.e. subdural or subarachnoid) or extradural space. This may derive from outside the body, or by communication with other body compartments, for example in the case of pneumothorax or surgical emphysema. It has been postulated that as cerebrospinal fluid (CSF) flows out of the subarachnoid space through a dural‐arachnoid breach, negative pressure is created within the epidural space. This negative pressure prevents the leakage of more CSF, until air enters to take its place and the pressure differential equilibrates [3].

The most common causes of pneumorrhachis are traumatic or iatrogenic injuries, for example during surgery or anaesthesia (traumatic nasotracheal intubation, spinal or epidural procedures) or diagnostic interventions [4]. Other causes include inflammation, degeneration, malignancy or infection with gas‐forming organisms, as well as conditions that lead to high intrathoracic pressure or barotrauma, such as severe asthma, cardiopulmonary resuscitation or severe emesis. Symptoms may include cervical myelopathy, radicular pain, paraplegia, headache or neck pain, due to the pressure effects of pneumorrhachis or pneumocephalus [5].

Here, we describe a case of symptomatic pneumorrhachis, presenting as position‐dependent hemiparesis following spinal surgery, which was successfully treated with conservative management.

Case report

A 66‐year‐old, right‐handed man presented with a nine‐month history of right upper limb pain and weakness. On examination, he had Medical Research Council (MRC) grade 4/5 weakness of shoulder abduction, extension and flexion, as well as weakness in elbow flexion in the right upper limb. Magnetic resonance imaging (MRI) demonstrated an intradural/extramedullary lesion at the level of the fourth cervical vertebra (C4) with evidence of spinal cord compression and the patient was scheduled for an excision of the lesion.

General anaesthesia was induced and maintained with target‐controlled infusions of propofol and remifentanil. Invasive blood pressure monitoring was used to ensure adequate spinal cord perfusion pressure. The patient was positioned prone with the table angled at 15° of cranial elevation. Following a C4 laminoplasty, a midline durotomy was performed with a lateral ‘trap door’ extension of the dural flap to the right, in order fully view the tumour and overlying nerve roots. The tumour and its ventral dural origin were excised. The dorsal dura was then sutured closed in a watertight fashion with fibrin glue overlaid (Fig. 1a). A subsequent Valsalva manoeuvre confirmed a watertight dural closure. Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were normal throughout the case.

Figure 1.

(a) Image from intraoperative recording showing dura sutured; (b) axial T1 MRI scan of the cervical and thoracic spine showing intraspinal air; (c) parasagittal bone window CT scan showing copious intraspinal gas

At the end of the procedure, the patient’s trachea was extubated and physical examination elicited full power in all four limbs before transfer to the recovery area. Thirty minutes later, the nurse caring for the patient observed the patient to have a right‐sided hemiplegia. The patient was reviewed 15 min later and power was assessed at MRC grade 3/5 in the right upper limb and MRC grade 5/5 in the right lower limb. Urgent MRI of the cervical spine demonstrated extensive extradural air, a small amount of intradural air and excluded any haematoma, cord oedema or infarction (Fig. 1b).

By the time the MRI scan had been performed, power had returned to normal in the upper and lower limbs. The patient was admitted to the High Dependency Unit (HDU) for further neurological monitoring. On HDU admission, the patient again developed upper limb weakness that was less profound than previously (MRC grade 4/5). A computed tomography (CT) scan of the head and the cervical and thoracic spine confirmed copious gas in the extradural space tracking from the upper thoracic level to the skull base, and a few flecks in the intrathecal space and the soft tissue (Fig. 1c). The patient was given 16 mg of dexamethasone i.v., oxygen via facemask at a rate of 4–6 l.min^‐1 and the mean arterial blood pressure was maintained at approximately 80 mmHg.

Both episodes of weakness were associated with turning the patient onto his left side, so he was positioned supine which resulted in improvement in his symptoms. The patient remained stable over the next 2 days and was discharged on the third day with residual weakness of right shoulder abduction of MRC grade 4/5.

Six weeks following surgery, the patient reported that his numbness and pain had completely resolved. Subjective weakness of his right shoulder abduction remained, but objective assessment of power noted improvement to MRC grade 5/5. The tumour histology was reported as a grade 1 meningioma. Magnetic resonance imaging performed three months after surgery demonstrated complete resolution of pneumorrhachis and no residual or recurrent meningioma.

Discussion

In spinal surgery, once the dura is breached, air can enter the intrathecal space, potentially leading to pneumorrhachis. Prone positioning increases intra‐abdominal pressure, which further increases the chance of pneumorrhachis occurring. Once trapped, air can move cranially or caudally depending on the position of the patient.

The risk of pneumorrhachis can be reduced by positioning the patient to ensure that the dural defect sits at the highest point, allowing air to escape; filling the surgical site with saline at the time of dural closure to displace the intradural air; and by confirming complete dural closure by performing a Valsalva manoeuvre [3]. All these steps were followed meticulously in this case and tissue adhesive was used to seal the dura, in addition to the sutures which had already produced a watertight seal, as later verified by intraoperative video recordings. It is possible that a very small defect in the dura produced a ball‐valve mechanism to draw air into the intradural space, from which it was unable to escape. At body temperature, the air bubble would have expanded.

The initial symptoms can be explained by air in the intrathecal as well as extradural space as seen on MRI. The patient made a good neurological recovery before transfer to HDU, indicating that some of the air was displaced or absorbed. Computed tomography imaging showed that mainly extradural air remained after 2 h, and there was an interval reduction in the volume of intraspinal gas.

The patient’s condition improved when he was positioned lying flat and worsened with left lateral positioning. We believe that these rapidly progressive neurological defects, largely provoked by positional changes, could be explained by movement of a hypodense air bubble causing compression to adjacent nerve roots within the restrictive space of the spinal canal.

Pneumorrhachis following spinal surgery does not always lead to neurological deficits (Table 1). We hypothesise that the serious nature of the neurological sequelae in this case may have occurred because our patient had intradural surgery, resulting in the subarachnoid space being in communication with room air for a prolonged period. It is also compounded by the fact that the patient had a pre‐operative neurological compromise and spinal cord manipulation during surgery. Trapped air adjacent to this vulnerable section of the cord may have led to more profound clinical effects.

Table 1.

Summary of the literature describing pneumorrhachis after spinal surgery

Author	Age	Sex	Symptom onset	Symptoms	Surgical spinal level	CSF leak	Infection	Management
Karavelioglu et al. [3]	56	M	Day 1	Headache, nausea	L3‐L5	No	No	Conservative
Keiser et al. [6]	59	M	2.5 months	Headache, dysarthria	T6‐L1	Yes	Yes	Wire removal, repair of dura
Uemura et al. [7]	59	M	Day 11	Paraparesis following lumbar puncture	T2‐T3	Yes	No	Decompression, repair of dura
Akyüz et al. [4]	62	F	2.5 months	Confusion	L5‐S1	X	Yes	Surgical duraplasty, antibiotic therapy
Yun et al [8]	59	M	Day 1	Headache, dizziness	L4‐L5	Yes	No	Conservative
Rovlias et al. a [9]	64	F	Immediate	Motor weakness, saddle anaesthesia	L4‐L5	Yes	No	Re‐operation, insertion of catheter for saline washout
Current case a	66	M	Immediate	Fluctuating reduction in limb power	C4	No	No	Conservative

F, Female; M, Male. Spinal Levels T, Thoracic; L, Lumbar; X, Information not available.

^a Spinal signs following pneumorrhachis as a result of spinal surgery.

Following the reduction in limb power that occurred in recovery area, several differential diagnoses were contemplated. Cerebral infarction and haemorrhage were considered; however, there was no facial droop, power in the limbs improved rapidly and the patient’s cardiovascular parameters were stable throughout. Spinal haematoma and oedema related to surgery were considered as possible causes of neurological deficit; however, both were excluded on MRI. The decision to not to re‐explore the surgical site for haematoma before obtaining imaging prevented the unnecessary risks of undertaking such a procedure. Spinal cord ischaemia or iatrogenic neurological trauma could be a differential diagnosis; however, the patient had an uneventful intraoperative course from a surgical, anaesthetic and neurophysiological point of view. The vital organ perfusion pressures were well maintained, there were no episodes of hypotension and SSEPs and MEPs were normal throughout the procedure. Postoperative MRI as well as CT scan did not show any cord abnormalities. Due to these factors, spinal cord ischaemia or iatrogenic cord injury was excluded.

Spontaneous absorption of the air in the spinal canal occurs in 85% of cases [2]. This means that in most instances, pneumorrhachis is asymptomatic and resolves quickly, and may therefore go undetected. The general management approach to symptomatic pneumorrhachis is supportive treatment comprising good hydration, bed rest, high‐concentration oxygen, correct positioning, appropriate antibiotics and administration of analgesics as required. It is advisable to avoid Valsalva manoeuvres such as nose‐blowing and coughing. Pneumorrhachis may be associated with significant pneumocephalus leading to headaches and confusion which may require specific management.

Supplementary oxygen increases the gradient for reabsorption of nitrogen between the pneumorrhachis and body tissues as the relatively insoluble nitrogen in the air bubble is replaced by oxygen which has higher solubility in body tissues. This reduces the total volume and pressure of air pockets and improves symptoms [10]. Ordinarily, in recovery area, a head‐up position offers optimal respiratory mechanics; however, in this case, this led to deterioration in the patient’s neurology due to cephalad migration of air. Optimal patient positioning is important until all nitrogen in the spinal canal is exchanged with oxygen and absorbed.

Surgical exploration and insertion of catheter for saline washout for pneumorrhachis has been described [10]. However, as this case demonstrates, if air does not continue to enter the spinal canal, conservative management can achieve a good outcome.